1. Field of the Invention
This invention relates to a physical-quantity detection sensor such as a pressure sensor. This invention also relates to a physical-quantity detection apparatus. This invention further relates to a sensor-signal processing apparatus.
2. Description of the Related Art
U.S. Pat. No. 6,040,779 discloses monitoring of the function of a symmetrical sensor bridge circuit which is performed in that the signal from the positive or negative half-bridge is subtracted from half the bridge supply voltage in a summing member and is subsequently amplified by an amplifier in such a way that it corresponds to the full bridge signal. The full bridge signal is compared with the amplified difference signal in a comparator. If the difference signal deviates in an unacceptable manner from the full bridge signal, the comparator switches an alarm signal on the output signal of the sensor so that this output signal is placed into a range which lies outside of the normal operational range of the sensor.
PCT application publication number WO 96/22515 discloses a semiconductor pressure transducer which comprises a silicon die having a topside and a bottom side. The silicon die further has a cavity in the bottom side, thereby forming a diaphragm. Four piezoresistive elements are disposed on the topside of the silicon die on a periphery of the diaphragm and connected via metalized conductors disposed on the silicon die in the form of a Wheatstone bridge. A plurality of bonding pads disposed on the topside of the silicon die provides external access to the Wheatstone bridge circuit. A diagnostic conductor is disposed on the topside of the silicon die such that the periphery of the diaphragm is crossed, the diagnostic conductor being connected to corresponding bonding pads at each of the diagnostic conductor. Thus, when the diaphragm ruptures, the diagnostic conductor ruptures thereby providing a positive indication of the rupture of the diaphragm by external circuitry in which the diagnostic conductor is used.
Japanese patent application publication number 2000-146991 corresponding to European patent application EP 0962748 A1 discloses monitoring of the function of a sensor component. The monitoring in Japanese application 2000-146991 is of an extended version designed to identify a change of ambient conditions and to timely take a countermeasure against an operation stop. In Japanese application 2000-146991, a sensor component is formed in a monolithic integral circuit, and has a sensor and at least one measurement amplifier. The sensor component is provided with external terminals for at least the feed of a current and an output measurement signal. Furthermore, an evaluation circuit is provided in the sensor component, and is connected to at least a circuit internal measurement point. The evaluation circuit is connected to a modulator for modulating at least one of a fed current, a fed voltage, and the output measurement signal. A diagnosis signal generated from circuit internal measurement values is fed out from an existing external connection terminal in the sensor component.
Japanese patent application publication number 10-506718 corresponding to PCT application publication number WO 97/05464 discloses a sensor having a diaphragm. In the sensor of Japanese application 10-506718, first and second resistance measurement bridges are placed on first and second half areas of the diaphragm, respectively. Two bridge signals generated by the first and second resistance measurement bridges are compared to check the function of the sensor and to detect a malfunction of the sensor.
Japanese patent application publication number 61-155931 discloses a pressure sensor including a first diaphragm and a second diaphragm. The first diaphragm supports a sensor member, and can deform in response to a pressure to be detected. The first diaphragm defines a reference pressure chamber. The second diaphragm supports a checking sensor member for generating a signal corresponding to a leakage from the reference chamber. The second diaphragm separates the reference pressure chamber from a checking pressure chamber. The checking sensor member is placed in the reference pressure chamber.
Japanese patent application publication number 8-247881 discloses a pressure difference sensor with a diagnosis function. In the sensor of Japanese application 8-247881, a bridge is composed of gauge resistors whose resistances vary in response to a distortion depending on a pressure to be detected. An energizing power supply is connected with the bridge. Two signals which appear at respective legs of the bridge are added into an addition result signal. The addition result signal is compared with a threshold level. When the addition result signal exceeds the threshold level, it is diagnosed that the sensor is abnormal.
Japanese patent application publication number 62-95485 discloses an apparatus designed so that an abnormality-indicating signal is outputted to an external when operation of a sensor is wrong. The apparatus of Japanese application 62-95485 includes a sensor power supply and a sensor portion which are connected to each other via a power feed line and an output signal line. The sensor portion has a carrier generation circuit and a carrier superimposing circuit. The carrier generation circuit acts to generate a radio-frequency signal (a carrier). The carrier generation circuit is activated and deactivated in response to whether or not a sensor circuit is normal. The carrier superimposing circuit operates to superimpose the radio-frequency signal (the carrier) on electric power supplied along the power feed line. The sensor power supply has a carrier sensing circuit for detecting the presence and absence of the carrier superimposed on the electric power supplied along the power feed line. The carrier sensing circuit outputs a signal to an external which indicates whether or not the sensor is normal.
Japanese patent application publication number 10-300615 discloses an on-line self diagnosis on a semiconductor pressure sensor including a diaphragm. In Japanese application 10-300615, the sensor is designed to output two signals. The two output signals from the sensor are inputted into a microcomputer on a time sharing basis, and are processed thereby. The signal processing by the microcomputer is designed to detect a damage to the diaphragm, a damage to a sensor connector, ageing-based variations in the conditions of a sensing portion and a circuit portion of the sensor, an ageing-based variation in the sensor sensitivity, and a variation in the zero point of the sensor.
Japanese patent application publication number 3-210047 discloses a sensor abnormality diagnosis apparatus. In the apparatus of Japanese application 3-210047, a sensor uses a power supply voltage as a reference voltage, and a pull-up resistor is subjected to the power supply voltage. The pull-up resistor may be replaced by a pull-down resistor connected to the ground. A current driven into the sensor is changed by varying the resistance of the pull-up resistor or the pull-down resistor. Detection is made as to a quantity of a variation in an output voltage from the sensor which occurs when the current driven into the resistor is changed. The detected variation quantity is compared with a reference variation quantity represented by data stored in a memory. The reference variation quantity is available when the sensor is normal. When the detected variation quantity is greater than the reference variation quantity, the sensor is diagnosed as being abnormal.
Japanese patent application publication number 9-304427 discloses a physical-quantity detecting apparatus which includes an acceleration sensor having a sensing portion and a diagnosing portion. The sensing portion detects an acceleration as a physical quantity, and outputs a signal depending on the detected acceleration. The diagnosing portion implements a diagnosing process of deciding whether the sensing portion is normal or abnormal in response to the output signal therefrom. On the basis of the result of the diagnosing process, the diagnosing portion changes a current flowing through a power supply terminal. From a voltage depending on the current flowing through the power supply terminal, a microcomputer gets information of the result of the diagnosing process.
It is a first object of this invention to provide an improved physical-quantity detection sensor.
It is a second object of this invention to provide an improved physical-quantity detection apparatus.
It is a third object of this invention to provide an improved sensor-signal processing apparatus.
A first aspect of this invention provides a physical-quantity detection sensor comprising a sensor portion (10) for generating and outputting a voltage depending on a physical quantity; a signal processing circuit (4) for processing the voltage outputted from the sensor portion (10) to generate and output a voltage depending on the voltage outputted from the sensor portion (10) during a physical-quantity sensing mode of operation; means for inputting a reference voltage into the signal processing circuit (4) during a checking mode of operation which differs from the physical-quantity sensing mode of operation, the reference voltage being different from the voltage outputted from the sensor portion (10); and means for, during the checking mode of operation, detecting a malfunction of the signal processing circuit (4) on the basis of an output signal from the signal processing circuit (4) which responds to the reference voltage inputted thereinto.
A second aspect of this invention provides a physical-quantity detection sensor comprising a sensor portion (10) for generating and outputting a voltage depending on a physical quantity; a signal processing circuit (4); a checking signal generation portion (20) for outputting a reference voltage for check; means for, during a physical-quantity sensing mode of operation, inputting the voltage outputted from the sensor portion (10) into the signal processing circuit (4) to implement detection of the physical quantity; means for, during a checking mode of operation which differs from the physical-quantity sensing mode of operation, inputting the reference voltage into the signal processing circuit (4) from the checking signal generation portion (20); and means for, during the checking mode of operation, detecting a malfunction of the signal processing circuit (4) on the basis of an output signal from the signal processing circuit (4) which responds to the reference voltage inputted thereinto.
A third aspect of this invention provides a physical-quantity detection sensor comprising a sensor portion (10) for generating and outputting a voltage depending on a physical quantity; a signal processing circuit (4); a checking signal generation portion (20) for outputting a reference voltage for check; means for, during a physical-quantity sensing mode of operation, selecting the voltage outputted from the sensor portion (10) and inputting the selected voltage into the signal processing circuit (4); and means for, during a checking mode of operation which differs from the physical-quantity sensing mode of operation, selecting the reference voltage outputted from the checking signal generation portion (20) and inputting the reference voltage into the signal processing circuit (4).
A fourth aspect of this invention is based on the second aspect thereof, and provides a physical-quantity detection sensor wherein the checking signal generation portion (20) comprises a Wheatstone bridge circuit including a tetragonal closed circuit having a series combination of resistors, and means for outputting a difference between voltages at opposite junctions in the Wheatstone bridge circuit as the reference voltage.
A fifth aspect of this invention is based on the fourth aspect thereof, and provides a physical-quantity detection sensor wherein the checking signal generation portion (20) comprises a constant-current circuit (21) for controlling a current in the Wheatstone bridge circuit.
A sixth aspect of this invention is based on the fifth aspect thereof, and provides a physical-quantity detection sensor further comprising a memory (22) storing data related to a current, and means for controlling the constant-current circuit (21) in response to the data stored in the memory (22).
A seventh aspect of this invention is based on the second aspect thereof, and provides a physical-quantity detection sensor wherein the checking signal generation portion (20) comprises a D/A conversion circuit of an R-2R ladder structure.
An eighth aspect of this invention is based on the second aspect thereof, and provides a physical-quantity detection sensor further comprising an analog multiplexer for inputting the voltage outputted from the sensor portion (10) into the signal processing circuit (4) during the physical-quantity sensing mode of operation, and for inputting the reference voltage into the signal processing circuit (4) from the checking signal generation portion (20) during the checking mode of operation.
A ninth aspect of this invention is based on the first aspect thereof, and provides a physical-quantity detection sensor wherein the signal processing circuit (4) comprises means for amplifying the voltage outputted from the sensor portion (10), and means for compensating for an offset and an offset-temperature-characteristic of the sensor portion (10).
A tenth aspect of this invention is based on the ninth aspect thereof, and provides a physical-quantity detection sensor further comprising comparing means (33) for, during the checking mode of operation, comparing the output signal from the signal processing circuit (4) with a predetermined reference signal, and means for, during the checking mode of operation, detecting a malfunction of the signal processing circuit (4) on the basis of a result of the comparing by the comparing means.
An eleventh aspect of this invention is based on the tenth aspect thereof, and provides a physical-quantity detection sensor further comprising means (34) for generating an output voltage which depends on whether or not a malfunction of the signal processing circuit (4) is detected on the basis of the result of the comparing by the comparing means (33).
A twelfth aspect of this invention is based on the first aspect thereof, and provides a physical-quantity detection sensor further comprising a diagnosis command signal generating portion for outputting a diagnosis command signal which provides change between the physical-quantity sensing mode of operation and the checking mode of operation.
A thirteenth aspect of this invention is based on the twelfth aspect thereof, and provides a physical-quantity detection sensor wherein the diagnosis command signal generating portion comprises a load (352) subjected to a prescribed power supply voltage; a transistor (351) connected in series with the load; first and second resistors (R1, R2) for generating a voltage which controls the transistor; and means for outputting a voltage at a junction between the load and the transistor as the diagnosis command signal.
A fourteenth aspect of this invention is based on the first aspect thereof, and provides a physical-quantity detection sensor further comprising a first memory for storing corrective data for the signal processing circuit and corrective data for the sensor portion, a second memory for storing corrective data for the signal processing circuit, and means provided in the signal processing circuit for using the corrective data stored in the second memory during the checking mode of operation.
A fifteenth aspect of this invention is based on the fourteenth aspect thereof, and provides a physical-quantity detection sensor further comprising a chip on which the signal processing circuit and the sensor portion are formed.
A sixteenth aspect of this invention is based on the first aspect thereof, and provides a physical-quantity detection sensor further comprising a memory for storing corrective data for the signal processing circuit, and means provided in the signal processing circuit for using the corrective data stored in the memory during the physical-quantity sensing mode of operation and the checking mode of operation.
A seventeenth aspect of this invention is based on the sixteenth aspect thereof, and provides a physical-quantity detection sensor further comprising a first chip on which the sensor portion is formed, a second chip on which the signal processing circuit is formed, the second chip differing from the first chip, the memory being formed on the second chip.
An eighteenth aspect of this invention is based on the first aspect thereof, and provides a physical-quantity detection sensor further comprising an output circuit (34) for generating a voltage signal in response to the output signal from the signal processing circuit (4), a comparator (33) for comparing the voltage signal generated by the output circuit (34) with a predetermined reference signal to detect a malfunction of the signal processing circuit (4) during the checking mode of operation, and means for controlling the output circuit (34) in response to a result of the comparing by the comparator (33) to cause the output circuit (34) to generate an output voltage which depends on whether or not a malfunction of the signal processing circuit (4) is detected.
A nineteenth aspect of this invention is based on the first aspect thereof, and provides a physical-quantity detection sensor further comprising a comparator (33) for comparing the output signal from the signal processing circuit (4) with a predetermined reference signal to detect a malfunction of the signal processing circuit (4) during the checking mode of operation, and outputting a signal representing whether or not a malfunction of the signal processing circuit (4) is detected during the checking mode of operation.
A twentieth aspect of this invention provides a physical-quantity detection sensor comprising a sensor portion (10) for generating and outputting a voltage depending on a physical quantity; a signal processing circuit (4); a checking signal generation portion (20) including a bridge circuit for outputting a reference voltage for check which is insensitive to the physical quantity; means for, during a physical-quantity sensing mode of operation, inputting the voltage outputted from the sensor portion (10) into the signal processing circuit (4) to implement detection of the physical quantity; means for, during a checking mode of operation which differs from the physical-quantity sensing mode of operation, inputting the reference voltage into the signal processing circuit (4) from the checking signal generation portion (20); and a system control circuit for, during the checking mode of operation, detecting a malfunction of the signal processing circuit (4) on the basis of an output signal from the signal processing circuit (4) which responds to the reference voltage inputted thereinto.
A twenty-first aspect of this invention provides a physical-quantity detection sensor comprising a sensor portion (510) for generating and outputting a voltage depending on a physical quantity; a checking signal generation portion (520) for outputting a reference voltage for check; a signal processing circuit (504, 533); means for, during a physical-quantity sensing mode of operation, selecting the voltage outputted from the sensor portion and inputting the selected voltage into the signal processing circuit; means for, during a checking mode of operation after the physical-quantity sensing mode of operation, selecting the reference voltage outputted from the checking signal generation portion and inputting the reference voltage into the signal processing circuit; and means (534) for continuously outputting a sensor output signal during the checking mode of operation, the sensor output signal being an output signal from the signal processing circuit occurring at a moment in the physical-quantity sensing mode of operation which immediately precedes the checking mode of operation.
A twenty-second aspect of this invention is based on the twenty-first aspect thereof, and provides a physical-quantity detection sensor wherein the continuously outputting means comprises means (534) for latching an output signal from the signal processing circuit at a moment in the physical-quantity sensing mode of operation which immediately precedes the checking mode of operation, and continuously outputting the latched signal as the sensor output signal during the checking mode of operation.
A twenty-third aspect of this invention is based on the twenty-second aspect thereof, and provides a physical-quantity detection sensor wherein the checking signal generation portion comprises a Wheatstone bridge circuit including a tetragonal closed circuit having a series combination of resistors (523, 524, 525, 526), and means for outputting a difference between voltages at opposite junctions (529, 530) in the Wheatstone bridge circuit as the reference voltage.
A twenty-fourth aspect of this invention is based on the twenty-third aspect thereof, and provides a physical-quantity detection sensor wherein the checking signal generation portion comprises a constant-current circuit (521) for controlling a current in the Wheatstone bridge circuit.
A twenty-fifth aspect of this invention is based on the twenty-fourth aspect thereof, and provides a physical-quantity detection sensor further comprising a memory (522) storing data related to a current, and means for controlling the constant-current circuit (521) in response to the data stored in the memory (522).
A twenty-sixth aspect of this invention is based on the twenty-second aspect thereof, and provides a physical-quantity detection sensor wherein the checking signal generation portion comprises a D/A conversion circuit of an R-2R ladder structure.
A twenty-seventh aspect of this invention is based on the twenty-second aspect thereof, and provides a physical-quantity detection sensor further comprising an analog multiplexer (503) for inputting the voltage outputted from the sensor portion into the signal processing circuit during the physical-quantity sensing mode of operation, and for inputting the reference voltage into the signal processing circuit from the checking signal generation portion during the checking mode of operation.
A twenty-eighth aspect of this invention provides a physical-quantity detection sensor comprising a sensor portion (510) for generating and outputting a voltage depending on a physical quantity; a checking signal generation portion (520) for outputting a reference voltage for check; a signal processing circuit (504, 533); means for, during a physical-quantity sensing mode of operation, inputting the voltage outputted from the sensor portion into the signal processing circuit; means for, during a checking mode of operation after the physical-quantity sensing mode of operation, inputting the reference voltage into the signal processing circuit from the checking signal generation portion; means for, during the checking mode of operation, detecting a malfunction of the signal processing circuit on the basis of an output signal from the signal processing circuit which responds to the reference voltage inputted thereinto; and means (534) for latching the output signal from the signal processing circuit at a moment in the physical-quantity sensing mode of operation which immediately precedes the checking mode of operation, and continuously outputting the latched signal during the checking mode of operation.
A twenty-ninth aspect of this invention is based on the twenty-eighth aspect thereof, and provides a physical-quantity detection sensor wherein the signal processing circuit comprises an amplifier (504) for amplifying the voltage outputted from the sensor portion, and an A/D converter (533) for converting an output signal of the amplifier into a corresponding digital signal, and the latching means comprises means for latching the digital signal generated by the A/D converter at a moment in the physical-quantity sensing mode of operation which immediately precedes the checking mode of operation, and continuously outputting the latched digital signal during the checking mode of operation.
A thirtieth aspect of this invention is based on the twenty-ninth aspect thereof, and provides a physical-quantity detection sensor further comprising a memory (537) for storing reference data, a comparator (538) for comparing the digital signal generated by the A/D converter with the reference data stored in the memory, and means for detecting a malfunction of the signal processing circuit in response to a result of the comparing by the comparator.
A thirty-first aspect of this invention is based on the thirtieth aspect thereof, and provides a physical-quantity detection sensor further comprising a D/A converter (535) for converting the digital signal generated by the A/D converter into an analog signal, an output circuit (536) for generating a voltage depending on the analog signal generated by the D/A converter, and means for, when a malfunction of the signal processing circuit is detected in response to the result of the comparing by the comparator, controlling the output circuit to output a voltage indicating the malfunction of the signal processing circuit.
A thirty-second aspect of this invention is based on the thirty-first aspect thereof, and provides a physical-quantity detection sensor wherein the voltage outputted by the output circuit when a malfunction of the signal processing circuit is detected is outside a prescribed range for the voltage generated by the output circuit during the physical-quantity sensing mode of operation.
A thirty-third aspect of this invention is based on the twenty-first aspect thereof, and provides a physical-quantity detection sensor further comprising a first memory for storing corrective data for the signal processing circuit and corrective data for the sensor portion, a second memory for storing corrective data for the signal processing circuit, and means provided in the signal processing circuit for using the corrective data stored in the second memory during the checking mode of operation.
A thirty-fourth aspect of this invention is based on the thirty-third aspect thereof, and provides a physical-quantity detection sensor further comprising a chip on which the signal processing circuit and the sensor portion are formed.
A thirty-fifth aspect of this invention provides a physical-quantity detection apparatus comprising a first sensor circuit (710) including a first sensing portion (711) for generating and outputting a signal depending on a physical quantity; reference generation means (720) for generating a reference signal (V1, V2) depending on the physical quantity; comparing means (730) for comparing the signal outputted by the first sensor circuit with the reference signal generated by the reference generation means; and means for generating a malfunction detection signal on the basis of a result of the comparing by the comparing means.
A thirty-sixth aspect of this invention is based on the thirty-fifth aspect thereof, and provides a physical-quantity detection apparatus wherein the reference generation means (720) comprises a second sensor circuit (720) including a second sensing portion (721) for generating a signal representing an upper-limit reference value (V1) and a signal representing a lower-limit reference value (V2), and the comparing means comprises means for determining whether or not the signal outputted by the first sensor circuit is in a range between the upper-limit reference value and the lower-limit reference value.
A thirty-seventh aspect of this invention is based on the thirty-sixth aspect thereof, and provides a physical-quantity detection apparatus wherein the reference generation means (720) comprises a positive power supply terminal (701a) subjected to a power supply voltage, a series combination of resistors connected between the positive power supply terminal and an output terminal of the second sensor circuit for executing voltage division to generate the signal representing the upper-limit reference value, a ground terminal (701c), and a series combination of resistors connected between the ground terminal and the output terminal of the second sensor circuit for executing voltage division to generate the signal representing the lower-limit reference value.
A thirty-eighth aspect of this invention is based on the thirty-fifth aspect thereof, and provides a physical-quantity detection apparatus further comprising a first terminal (701a), means for applying a power supply voltage (Vcc) to the first sensor circuit via the first terminal, and current controlling means (740) connected to the first terminal for varying a current in response to the result of the comparing by the comparing means, and generating the malfunction detection signal on the basis of a variation in a current flowing through the first terminal.
A thirty-ninth aspect of this invention is based on the thirty-eighth aspect thereof, and provides a physical-quantity detection apparatus further comprising a second terminal (701b) for the signal outputted by the first sensor circuit, and a third terminal (701c) connected to a ground.
A fortieth aspect of this invention is based on the thirty-eighth aspect thereof, and provides a physical-quantity detection apparatus wherein the reference generation means (720) comprises a second sensor circuit (720) including a second sensing portion (721) for generating a signal representing an upper-limit reference value (V1) and a signal representing a lower-limit reference value (V2), and the comparing means comprises means for determining whether or not the signal outputted by the first sensor circuit is in a range between the upper-limit reference value and the lower-limit reference value, and wherein the current controlling means comprises a first element (742), a second element (743, 744), means responsive to the result of the comparing by the comparing means for enabling a current to flow through the first element and inhibiting a current from flowing through the second element when the signal outputted by the first sensor circuit is in the range between the upper-limit reference value and the lower-limit reference value, means responsive to the result of the comparing by the comparing means for inhibiting a current from flowing through the first element and enabling a current to flow through the second element when the signal outputted by the first sensor circuit is not in the range between the upper-limit reference value and the lower-limit reference value, and means for generating the malfunction detection signal on the basis of a variation in a current flowing through the first element and a variation in a current flowing through the second element.
A forty-first aspect of this invention provides a physical-quantity detection apparatus comprising a first sensor circuit (710) including a first sensing portion (711) for generating and outputting a signal depending on a physical quantity; reference generation means (720) for generating a reference signal (V1, V2) depending on the physical quantity; comparing means (730) for comparing the signal outputted by the first sensor circuit with the reference signal generated by the reference generation means; and means for outputting information of a result of the comparing by the comparing means via power fed to the first sensor circuit.
A forty-second aspect of this invention is based on the forty-first aspect thereof, and provides a physical-quantity detection apparatus further comprising a first terminal (701a), means for applying a power supply voltage (Vcc) to the first sensor circuit via the first terminal, and current controlling means (740) connected to the first terminal for varying a current in response to the result of the comparing by the comparing means, and generating the information of the result of the comparing by the comparing means on the basis of a variation in a current flowing through the first terminal.
A forty-third aspect of this invention is based on the forty-first aspect thereof, and provides a physical-quantity detection apparatus wherein the reference generation means (720) comprises a second sensor circuit (720) including a second sensing portion (721) for generating a signal representing an upper-limit reference value (V1) and a signal representing a lower-limit reference value (V2), and the comparing means comprises means for determining whether or not the signal outputted by the first sensor circuit is in a range between the upper-limit reference value and the lower-limit reference value, and wherein the reference generation means (720) further comprises a positive power supply terminal (701a) subjected to a power supply voltage, a series combination of resistors connected between the positive power supply terminal and an output terminal of the second sensor circuit for executing voltage division to generate the signal representing the upper-limit reference value, a ground terminal (701c), and a series combination of resistors connected between the ground terminal and the output terminal of the second sensor circuit for executing voltage division to generate the signal representing the lower-limit reference value.
A forty-fourth aspect of this invention is based on the forty-third aspect thereof, and provides a physical-quantity detection apparatus wherein the second sensor circuit is higher in sensitivity than the first sensor circuit.
A forty-fifth aspect of this invention provides a sensor-signal processing apparatus comprising a power supply terminal; means for feeding, via the power supply terminal, a power supply voltage for operating a sensor; means for monitoring an output voltage from the sensor; current detecting means (759, 760) for generating a voltage depending on a current flowing through the power supply terminal; signal converting means (761) for converting the output voltage from the sensor into a first conversion-resultant signal, and converting the voltage generated by the current detecting means into a second conversion-resultant signal; and signal processing means (762) for processing the first conversion-resultant signal generated by the signal converting means, and detecting a malfunction of the sensor in response to the second conversion-resultant signal generated by the signal converting means.